1. Field of the Invention
This invention relates to a laser coagulation system, and more particularly to a laser coagulation system adapted for use in an ophthalmological treatment in which a laser beam from a laser source is radiated into a patient's eye to develop great heat causing thermal coagulation at a predetermined portion of the biological organism in the eyeball of a patient.
2. Description of the Prior Art
There have long been known laser coagulation systems in which during an ophthalmic operation against diseases such as retina detachment, glaucoma, etc., a patient's eye is irradiated with laser energy which is absorbed in a biological organism such as retina to develop thermal coagulation thereon for ophthalmological treatment. For this purpose, the laser coagulation system includes a laser beam projector for producing a laser beam from an argon or krypton laser, the laser beam being condensed to a predetermined diameter, directed toward a predetermined portion of the eyeball to be coagulated, and then focussed thereon as a laser spot for thermal coagulation.
The laser coagulation system further comprises a slit image projector for forming a slit image on the eyeball to illuminate the background and determine the predetermined portion of eyeball to be coagulated, and observation equipment for observing the slit image and laser spot in the eyeball.
In such prior laser coagulation systems, the slit image projector is provided with a mirror for directing the slit image toward the predetermined portion of the eye, while the laser beam projector is provided with a mirror for directing the laser beam toward the predetermined portion thereof. The mirror for the slit image projector is divided into upper and lower portions, behind which the mirror for the laser beam projector is arranged.
In this case, the slit image projector is arranged at the lower portion of the system and projects slit light, which is reflected by the two-divided mirror toward the selected portion of the eye to be coagulated, while the laser beam projector is arranged at the upper portion of the system and emits a laser beam, which is, after the reflection by the mirror, caused to pass through a gap between the upper and lower portions of the two-divided mirror, thereby forming a laser spot in the proximity of the slit image in the eyeball.
Thus, the laser coagulation system in the prior art has the drawback that the laser beam projector constitutes a different system from that of the slit image projector. This disadvantageously leads to a large-sized coagulation system. Furthermore, the mirror for the laser beam projector must be large enough to allow the formation of the laser spot of a greater diameter at portions other than the selected portion to be coagulated in order to provide a reduced energy density causing no coagulation. This also disadvantageously causes the mirror for the slit image projector to become smaller, thus resulting in the formation of a dark and blurred slit image.
In addition, the prior slit image projector employs a Keller illumination in which a lamp filament is imaged on the entrance pupil of a slit imaging lens. In this situation, the two-divided mirror of the slit image projector has a gap between the divided portions, so that the light illuminating the center of the entrance pupil may be caused to pass through the gap which results in reduced intensity of the slit image.